I was looking and found this Garmin page
http://www.garmin.com/support/commProtocol.html
It seems to be the start of the answer to the question
previously asked about transferring waypoints.
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Device Interface SDK
For advanced users desiring to develop their own
custom software applications for communicating with GarminŽ
GPS products, this document describes the communication
protocols required for transferring data including
waypoints, routes, and track logs to and from Garmin GPS
products via RS-232 or USB.
License Agreement
Warning: This documentation is provided on an
"as is" basis without warranty of any kind -- either
expressed or implied -- including, without limitation, any
implied warranties of merchantability or fitness for a
particular purpose.
The information contained within this
documentation is subject to change without notice.
In addition, no developer support will be
provided by Garmin concerning the information contained
within the documentation or implementation of this
information within your software application.
Download the Garmin Device Interface SDK
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